The present invention relates to automotive braking systems. More particularly, the brake assembly of the present invention includes a combined hydraulic service brake and electric park brake feature, which eliminates the need for a separate parking brake and associated structure.
In conventional automotive braking systems the service brake and the parking/emergency brake are separate systems. The service brake is used for normal braking function during operation of the vehicle. The service brake typically includes a master cylinder that converts a manual exertion of force on a brake pedal into an increase of hydraulic pressure. The hydraulic pressure acts on a remote wheel cylinder or slave cylinder causing a brake pad to be applied to an associated rotor connected to a wheel of the vehicle, thus slowing the vehicle. Conventional park brakes are typically engaged when the vehicle operator pulls a lever or depresses a pedal connected to the park brake by a steel cable.
Hydraulic brakes are generally not used as parking brakes because hydraulic fluid under constant pressure has a tendency to leak past seals of a hydraulic brake system over time resulting in a decrease in fluid pressure, which would cause the brake to release its hold on the rotor. Therefore, this inadequacy of the hydraulic brake for use as a parking brake has required the existence of two separate braking systems to fulfill the needs of a vehicle operator.
It would be desirable to have a brake system that would improve on the existing brake system.
One aspect of the invention provides a brake apparatus including a housing including a bore formed therein. A piston is slidably positioned in the bore. The piston and bore define a fluid chamber therebetween. A screw member is operably engaged with the piston, wherein the piston and screw member are movable based on fluid pressure in the fluid chamber and wherein the piston is movable in a linear direction based on the rotational movement of the screw member.
Other aspects of the invention provide the brake apparatus with a driving member positioned in the bore and operatively engaged with the screw member. A motor may be operatively engaged with the driving member. A transmission may be operatively engaged with the driving member and a motor may be operatively connected to the transmission. The screw member may include a first helically shaped groove formed into an outer surface of the screw member and the piston may include a second helically shaped groove formed into an inner surface of the piston, the first and second grooves positioned to engage a plurality of rolling elements disposed therebetween. The screw member may include a first threaded portion on an outer surface thereof, and the piston includes a second threaded portion on an inner surface thereof, the first and second threaded portions being threadably engaged. The driving member may include an extending portion operatively connected to the screw member. The brake apparatus may include a first seal disposed between the housing and the driving member, a second seal disposed between the housing and the piston and a third seal disposed within the piston.
Another aspect of the invention may provide a first seal disposed between the housing and the driving member, a second seal disposed between the housing and the piston and a third seal disposed within the piston, wherein the screw member includes a first helically shaped groove formed into an outer surface of the screw member, and the piston includes a second helically shaped groove formed into an inner surface of the piston, the first and second grooves positioned to engage a plurality of rolling elements disposed therebetween, the driving member including a driving portion operatively connected to the screw member.
Another aspect of the present invention provides a method of applying an electric park brake for a hydraulic apply brake system including rotating a screw member engaged with a piston and linearly advancing the piston into contact with a brake pad responsive to the rotation of the screw member.
Another aspect of the method of the present invention includes activating a motor to rotate the screw member. The method may include activating a motor to engage a transmission and activating the transmission to rotate the screw member.
Another aspect of the present invention provides a brake apparatus including a means for rotating a screw member operatively engaged with a piston and a means for linearly advancing the piston into contact with a brake pad responsive to the rotation of the screw member. Other aspects of the invention provide a brake apparatus including a means for activating a motor to engage a transmission and a means for activating the transmission to rotate the screw member.